More than one in four children in the United States is exposed to weapon-related violence -- as a victim or witness -- which ups their risk for mental health problems, a new study says.

Using 2011 data from a national survey of children and parents, researchers also estimated that one in 33 kids has been assaulted in incidents where lethal weapons -- guns and knives -- were used.

Such lethal weapons exposure makes it more likely they will arm themselves, or associate with people carrying weapons. They are also more likely to suffer long-term psychiatric consequences, the study authors said.

"Exposure to violence involving highly lethal weapons is associated with higher trauma symptoms, over and above exposure to all other types of violence, making it a strong contributor to adolescent depression, anxiety and aggression," said study co-author Kimberly Mitchell, a research assistant professor of psychology at the University of New Hampshire's Crimes Against Children Research Center.

"These are problems pediatricians encounter often in their practices," she added.

Kids exposed to weapons-related violence are also more likely than others to experience seven or more types of victimization in the prior year, the researchers found.

The study, published online June 8 in the journal Pediatrics, focused on more than 4,100 children from 2 to 17 years old who participated in a telephone survey. (Parents or caregivers answered questions for those younger than 10.)

Based on the responses, researchers estimated that more than 17.5 million children in the United States have experienced violence involving weapons such as guns, knives, rocks and sticks.

But exposure to lethal weapons had the strongest consequences, the researchers found.

Moreover, witnessing an incident involving a lethal weapon is as traumatic as being the victim, the researchers said.

"Our data -- not just in this paper but the whole National Survey of Children's Exposure to Violence research program -- shows that witnessing violence has just as many traumatic psychological consequences for kids," said study co-author Sherry Hamby, a research professor of psychology from Sewanee: University of the South.

"After all, just because the gun was pulled on someone else doesn't mean the witnesses aren't in danger, too," she said. "And sometimes what someone might describe as 'witnessing' involves actual physical danger or injury to kids as well."

Perhaps not surprisingly, said Mitchell, "We found youth living in what we're calling a 'weaponized environment' are more likely to report victimization with a weapon."

Specifically, kids exposed to gangs are twice as likely to report being a victim of violence involving a weapon, the study found. "The same was true for personal weapon-carrying," she said.

Ideally, Mitchell said, children would avoid environments where weapons are found. "Yet this might be difficult for some youth living in high-crime communities," she said.

"This points to the importance of a public health approach to this problem and looking for community- and policy-level solutions," Mitchell added.

Can these results be translated to children who "witness" violence with weapons in video games and movies? Not according to this particular survey, said the study authors, since the questions related to "real life" incidents, not television or video games.

The study results do not suggest that simply being exposed to guns and knives increases a child's risk of being traumatized. It is being exposed to violence using guns and knives that causes mental health trauma. The study states, "Positive firearm experiences for some youth may moderate or buffer the effects of victimization exposure."

One injury expert said the study results should prompt additional efforts to protect children from the harms of violence.

Dr. Patrick Carter, assistant professor of emergency medicine at the University of Michigan Injury Center, said measures are needed by individuals and communities "that decrease the exposure of children to firearm and other weapon-related violence and aid in preventing the negative long-term health-related consequences of such violence."

Hamby concluded: "The collateral damage from gun and knife violence extends well beyond the 'target' victim. Screening for weapon exposure should be standard practice for children receiving services for victimization."